1. Field of the Invention
The present invention relates to a biocontrol formulation, and relates in particular to a biocontrol formulation containing high concentration of viable Streptomyces spp. spores. The present invention also relates to a method for preparing the above biocontrol formulation and a method using the formulation.
2. Description of Related Art
The use of agrochemical formulations improved agricultural productivity and increased the world food supply in recent years. However, repeated and even misuses of agrochemical formulations for long periods have led to the development of catastrophic impact globally on the ecosystems. Major ecological impacts commonly encountered include chemical resistance of pests and pathogens, chemical residues, environmental pollution, and endangered wildlifes. The substantial ecological deterioration is often accused to be the major causes of problems such as cancer, dysplasia and malfunction of the human immune system.
Despite the great disadvantages of agrochemical applications, the needs for agrochemical formulations continue growing steadily under the pressure of increasing population and soaring food demands. During the past decade, the annual consumption of agrochemical compositions globally estimates over 30 billion US dollars. The disadvantages of conventional agrochemical applications stimulate the development of biorational biopesticides, which has become a main stream of biotechnology undertaking worldwide. Microbial biocontrol agents are among these endeavors attracted greatest attention because of the wide application, the excellent control effect, and the best of all is the bountiful supportive resources from microbial biotechnology.
Streptomyces spp. are widespread gram-positive bacteria. More than 400 species have been described, most of them produce antibiotics. For disease control of plants, members of Streptomyces spp. have been used for over half a century. Streptomycin was the first to discover from S. griseus in 1943 and successfully applied it to prevent bacterial infestations on fruit trees and vegetables. With the success of streptomycin application, the use of antibiotic metabolites derived from Streptomyces spp. later became a predominant art for the control of certain foliar diseases on plants. From 1950 to 1970, quite a few Streptomyces derived antibiotics had been launched; notable examples included the use of Blasticidin-S and Kasugamycin for the control of rice blast disease (Pyricularia oryzae Cav.), and the use of Polyoxin and Validamycin for the control of sheath blight disease of rice (Thanatephorus cucumeris (Frank) Donk).
Since 1970, the control of soil-borne diseases began to draw increasing attention in regarding to the employment of Streptomyces spp. for plant protection. Successful examples included the application for the control of root rot on pea caused by Rhizoctonia solani, Fusarium wilt on cucurbits and carnations caused by Fusarium oxysporum, postharvest disease of various crops caused by Aspergillus spp., and some other important diseases caused by Alternaria spp., Fusarium culmonum, Botrytis cinerea and Pythium ultimum. The antibiotics applied among these cases are in essence biochemical property which appears to be inhibitory or lethal to the pathogens.
However, the safety of antibiotic application in agriculture has been challenged lately due to the increasing concern of the development of antibiotic resistance in medical treatment. The application of antibiotics for plant disease control is thus now facing unprecedented pressure due to the over exaggerated concern of the social public about the developing and transferring of the antibiotic resistance among pathogenic microbial populations.
In contrast to the concerns and difficulties in the development of antibiotics, the development of microbial biomass products have attracted great attention recently. The numbers of commercialized microbial biomass products are increasing; their efficacy of disease control is satisfactory. The commercialized products with worldwide recognition, to name a few, include the fungal products of Gliocladium viride and Trichoderma spp., and the bacterial biomass products of Bacillus subtilis and Streptomyces griseus. The use of beneficial microbial biomass products has been a routine application for long time as an additive feed for aquatic animals or domestic animals. The direct fed microbial products, generally quoted as “probiotics”, used as additives in animal breeding are known having bioregulators function in an animal's body.
The efficacy of disease control by above mentioned microbial biomass products is featured by an interaction from multiple mechanisms including nutrient and space competition, antibiotic activity, improved nutrient availability and microbial diversity, improved plant growth and vigor, improved soil fertility and the enhanced disease resistance. It is worth to mention that the observed, antibiotic activity per se is contributed by the collective effect of cohorts of antibiotic derivatives rather than a single purified composition. The involvement of multiple mode of action offers great advantages that chemical resistance problems generally encountered in conventional chemical and biochemical pesticide application wouldn't likely to occur. What adds more value is that most of the microbial species used are beneficial for soil fertility and plant growth; their environmental-friendliness make them an ideal alternative tool for pest management especially where agricultural sustainability is taken into account.
For the success of development of a microbial biomass products, it is critical that (1) the isolated microorganisms must be generally regarded as safe (GRAS) for animals and humans; (2) the shelf life of the attempted product should be satisfactory when stored properly; (3) the field application should be convenient by common practices; and (4) the price, smell, and efficacy should be competitive for customer acceptance.
The development of Streptomyces spp. biocontrol formulation has been a hot topic for long time because the great potential for plant disease control. However, most of the existing art known so far has been devoted to explore the uses of antibiotics secreted. The only EPA registered Streptomyces spp. containing biomass product gaining wide recognition is Mycostop (Kemira Co. Ltd., Finland). Another product of this kind recently approved by EPA is Actinovate (Natural Industries Co. Ltd., USA). The product Mycostop is known to contain viable S. griseovirides mycelia and spores at the concentration of 108 cfu/g; it was recommended for the control of soil-borne plant diseases. Actinovate is a S. lyticus biomass containing water dispersible granule, it is also recommended for the control of soil-borne diseases.
For preparation of a Streptomyces spp. viable inoculants in a large scale, conventionally it is done by solid fermentation in which wheat, oat or unpolished rice grains are the predominant growth substrates used. Because liquid fermentation is a widely used, rapid and easy method appropriate for preparing microbial inoculants in large volumes, a liquid product would be more preferable. However, the preparation of Streptomyces spp. biomass product by liquid fermentation in large scale is of great difficulty since the bacteria grow predominantly as mycelia balls rather than spores.
The present invention discloses a novel method that solves the problem of preparing high concentration viable Streptomyces spp. spore inoculant in large scale by liquid fermentation.